1,721,070 research outputs found
Skin pigmentation: Is the control of melanogenesis a target within reach?
No full textSkin pigmentation represents one of the most peculiar traits of human beings and its alteration as a consequence of pathological conditions has a dramatic impact on the wellness of individuals and their social relationships. [...
Iron and copper ions accelerate and modify dopamine oxidation to eumelanin : implications for neuromelanin genesis
No full textDopamine (DA) is a precursor of neuromelanin (NM) synthesized in the substantia nigra of the brain. NM is known to contain considerable levels of Fe and Cu. However, how Fe and Cu ions affect DA oxidation to DA-eumelanin (DA-EM) and modify its structure is poorly understood. EMs were prepared from 500 mu M DA, dopaminechrome (DAC), or 5,6-dihydroxyindole (DHI). Autoxidation was carried out in the absence or presence of 50 mu M Fe(II) or Cu(II) at pH 7.4 and 37 . EMs were characterized by Soluene-350 solubilization analyzing absorbances at 500 nm (A500) and 650 nm (A650) and alkaline hydrogen peroxide oxidation (AHPO) yielding various pyrrole carboxylic acids. Pyrrole-2,3,4,5-tetracarboxylic acid (PTeCA) served as a molecular marker of cross-linked DHI units. Importantly, Fe and Cu accelerated DA oxidation to DA-EM and DHI oxidation to DHI-EM several-fold, whereas these metals only weakly affected the production of DAC-EM. The A500 values indicated that DA-EM contains considerable portions of uncyclized DA units. Analysis of the A650/A500 ratios suggests that Fe and Cu caused some degradation of DHI units of DA-EM during 72-h incubation. Results with AHPO were consistent with the A500 values and additionally revealed that (1) DA-EM is less cross-linked than DAC-EM and DHI-EM and (2) Fe and Cu promote cross-linking of DHI units. In conclusion, Fe and Cu not only accelerate the oxidation of DA to DA-EM but also promote cross-linking and degradation of DHI units. These results help to understand how Fe and Cu in the brain affect the production and properties of NM
Protection against ultraviolet radiation involves MC1R-mediated non-pigmentary and pigmentary mechanisms in vivo
No full textIndividuals with red hair and fair skin due to MC1R gene variants are at higher risk of cutaneous neoplasia, consistent with MC1R having a role in photoprotection. The exact reasons for greater UVR susceptibility as a result of compromised MC1R function are unclear, but hypotheses include reduced photoprotection due to less eumelanin, pheomelanin-induced phototoxicity, and lower protection by “non-pigmentary” MC1R effects. To determine how MC1R photoprotects, an in vivo hairless MC1R model containing Mc1r?/? albino, MC1R+Mc1r?/? albino, Mc1r?/? pigmented, and MC1R+Mc1r?/? pigmented mice was generated. After single doses of UVR, no significant differences in epidermal cyclobutane pyrimidine dimers or sunburn cell (SBC) formation were observed between pigmented and albino groups. However, after repeated UVR exposure, the number of p53 clones in albino skin was significantly elevated when this was null for MC1R. Furthermore, in the absence of functional MC1R, fewer p53 clones were observed in pigmented than in albino skin. The results indicate that MC1R protects by a combination of pigmentary and non-pigmentary effects in vivo and that when MC1R function is compromised the melanin type in skin is still protective against UVR
Going Beyond Counting First Authors in Author Co-citation Analysis
Get PDFThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Variations on the Author
Get PDF“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Appropriate Similarity Measures for Author Cocitation Analysis
Get PDFWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
Dispelling the Myths Behind First-author Citation Counts
Get PDFWe conducted a full-scale evaluative citation analysis study of scholars in the XML research field to explore just how different from each other author rankings resulting from different citation counting methods actually are, and to demonstrate the capability of emerging data and tools on the Web in supporting more realistic citation counting methods. Our results contest some common arguments for the continued
use of first-author citation counts in the evaluation of scholars, such as high correlations between author rankings by first-author citation counts and other citation
counting methods, and high costs of using more realistic citation counting methods that are not well-supported by the ISI databases. It is argued that increasingly available digital full text research papers make it possible for citation analysis studies to go beyond what the ISI databases have directly supported and to employ more
sophisticated methods
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